1. Field of the Invention
This invention relates to a process for the production of heat-resistant polyurethane compositions.
2. Description of the Prior Art
The invention concerns a process for the production of heat-resistant polyurethane elastomers from generally known starting components, in which an isocyanate-terminated adduct, produced from a principally linear polyol and a diisocyanate with relatively unreactive NCO groups or with isocyanate groups of different reactivity, is reacted with an aromatic diisocyanate of symmetrical structure and a chain extender.
Polyurethane elastomers based on high-molecular-weight polyols, diisocyanates and low-molecular-weight chain extenders are characterized by a balanced set of properties according to the state of the art and have therefore proved themselves to be highly useful in a number of applications.
Despite the advantages in mechanical properties and wear resistance, the polyurethane elastomers of the state of the art still have serious disadvantages which considerably limit their applications. These consist primarily of their inadequate heat stability, leading to early softening and thus to failure of parts subjected to high stress. This insufficient heat stability of the known materials has the result that parts under a dynamic stress, e.g., highly stressed runners, rolls or tires, already begin to soften at 50.degree.-80.degree. C, thus impairing and destroying their good properties This material characteristic thus far has considerably limited the introduction of polyurethane elastomers in fields in which the material is subjected to high dynamic as well as thermal loads.
Thus far, polyurethane elastomers with improved heat stability could be produced only with the use of very costly and less common starting materials, such as naphthalene-1,5-diisocyanate, or toxic materials, such as methylene-bis(2-chloroaniline).
For these reasons, considerable industrial interest exists in the development of polyurethane elastomers which no longer have these shortcomings and therefore have a broader field of application.